Class 9 – Chapter 7: Enzymes | MCQs (1–20)
Section 1: Basic Concepts of Enzymes
-
Enzymes are
a) Proteins
b) Carbohydrates
c) Fats
d) Vitamins
✅ Answer: a) Proteins -
Enzymes are produced by:
a) Ribosomes
b) Mitochondria
c) Chloroplast
d) Nucleus
✅ Answer: a) Ribosomes -
The function of enzymes is to
a) Destroy cells
b) Slow down reactions
c) Speed up reactions
d) None of these
✅ Answer: c) Speed up reactions -
The substance on which an enzyme acts is called:
a) Substrate
b) Inhibitor
c) Catalyst
d) Product
✅ Answer: a) Substrate -
The part of the enzyme where the substrate binds is
a) Nucleus
b) Active site
c) Passive site
d) Vacuole
✅ Answer: b) Active site -
Enzymes are made up of:
a) DNA
b) Lipids
c) Proteins
d) RNA
✅ Answer: c) Proteins -
Enzymes act as
a) Inhibitors
b) Catalysts
c) Products
d) Reactants
✅ Answer: b) Catalysts -
Which of the following affects enzyme activity?
a) Light
b) Sound
c) Temperature
d) Electricity
✅ Answer: c) Temperature -
Enzyme activity is maximum at:
a) Low temperature
b) Optimum temperature
c) Freezing point
d) High pressure
✅ Answer: b) Optimum temperature -
Enzymes are denatured at
a) Low temperature
b) High pressure
c) High temperature
d) Moderate temperature
✅ Answer: c) High temperature -
Enzymes work by:
a) Raising activation energy
b) Lowering activation energy
c) Blocking reactions
d) Breaking down DNA
✅ Answer: b) Lowering activation energy -
All enzymes are:
a) Lipids
b) Vitamins
c) Proteins
d) Sugars
✅ Answer: c) Proteins -
Enzymes are specific in:
a) Location
b) Substrate
c) Size
d) Shape only
✅ Answer: b) Substrate -
The enzyme that breaks down starch is
a) Protease
b) Lipase
c) Amylase
d) Lactase
✅ Answer: c) Amylase -
Enzymes are needed in:
a) Small amounts
b) Large amounts
c) Unlimited quantity
d) Daily
✅ Answer: a) Small amounts -
Which of these is a digestive enzyme?
a) Trypsin
b) Hemoglobin
c) Insulin
d) Keratin
✅ Answer: a) Trypsin -
Which of the following is not a characteristic of enzymes?
a) Reusable
b) Specific
c) Used up in reaction
d) Protein in nature
✅ Answer: c) Used up in reaction -
Which organ produces most digestive enzymes?
a) Brain
b) Pancreas
c) Heart
d) Kidney
✅ Answer: b) Pancreas -
Which factor does not affect enzyme action?
a) Temperature
b) pH
c) Light
d) Substrate concentration
✅ Answer: c) Light -
The enzyme lipase breaks down:
a) Proteins
b) Carbohydrates
c) Nucleic acids
d) Fats
✅ Answer: d) Fats
Section 2: Structure & Mechanism of Enzyme Action
-
The place where an enzyme binds to its substrate is called the:
a) Core
b) Active site
c) Binding cell
d) Reaction zone
✅ Answer: b) Active site -
The model describing enzyme-substrate interaction is
a) Passive model
b) Lock and key model
c) Puzzle model
d) Binding theory
✅ Answer: b) Lock and key model -
Enzymes reduce the ___________ energy needed for a reaction.
a) Binding
b) Kinetic
c) Activation
d) Heat
✅ Answer: c) Activation -
Which bond helps maintain the structure of enzymes?
a) Covalent bonds only
b) Ionic bonds only
c) Hydrogen bonds
d) Only peptide bonds
✅ Answer: c) Hydrogen bonds -
Which structural level of a protein is responsible for enzyme activity?
a) Primary
b) Secondary
c) Tertiary
d) Quaternary
✅ Answer: c) Tertiary -
An enzyme-substrate complex is:
a) A permanent bond
b) Temporary structure during a reaction
c) A type of sugar
d) An enzyme inhibitor
✅ Answer: b) Temporary structure during a reaction -
The enzyme-substrate complex is formed at the:
a) Cytoplasm
b) Active site
c) Mitochondria
d) Ribosome
✅ Answer: b) Active site -
After a reaction, the enzyme:
a) Is destroyed
b) Becomes part of the product
c) Detaches unchanged
d) Changes shape permanently
✅ Answer: c) Detaches unchanged -
The specificity of enzymes depends on
a) The number of substrates
b) The shape of the active site
c) The pH of solution
d) The number of products
✅ Answer: b) The shape of the active site -
The lock and key model was proposed by
a) Watson
b) Fischer
c) Mendel
d) Darwin
✅ Answer: b) Fischer -
An enzyme can act
a) Only once
b) Multiple times
c) Only on one type of reaction
d) Only when heated
✅ Answer: b) Multiple times -
In enzyme activity, what is released after the reaction?
a) Substrate
b) Product
c) Enzyme
d) Heat
✅ Answer: b) Product -
Which part of the enzyme changes shape in the induced fit model?
a) Substrate
b) Active site
c) Product
d) Whole enzyme
✅ Answer: b) Active site -
The term "enzyme-substrate complex" means:
a) Enzyme and product
b) Substrate and product
c) Enzyme bonded to substrate temporarily
d) Enzyme permanently destroyed
✅ Answer: c) Enzyme bonded to substrate temporarily -
A coenzyme is
a) A protein
b) A mineral
c) An organic helper molecule
d) A DNA segment
✅ Answer: c) An organic helper molecule -
Cofactors that help enzymes can be
a) Vitamins
b) Minerals
c) Both a and b
d) None of these
✅ Answer: c) Both a and b -
If the active site is altered, the enzyme becomes:
a) Faster
b) Inactive
c) Stronger
d) More efficient
✅ Answer: b) Inactive -
The induced fit model suggests that:
a) Enzyme remains rigid
b) Substrate forces the enzyme to fit
c) Enzyme molds around the substrate
d) Active site never changes
✅ Answer: c) Enzyme molds around the substrate -
Which condition can cause an enzyme’s active site to change shape?
a) Constant pH
b) Low substrate concentration
c) High temperature
d) Regular body temperature
✅ Answer: c) High temperature -
The catalytic activity of enzymes is dependent on:
a) Their color
b) Their 3D shape
c) Their DNA
d) Their weight
✅ Answer: b) Their 3D shape
Section 3: Types and Examples of Enzymes
-
Enzymes that break down proteins are called:
a) Amylases
b) Proteases
c) Lipases
d) Lactases
✅ Answer: b) Proteases -
The enzyme that digests starch is
a) Pepsin
b) Amylase
c) Lipase
d) Trypsin
✅ Answer: b) Amylase -
Lipase acts on:
a) Proteins
b) Sugars
c) Fats
d) DNA
✅ Answer: c) Fats -
Which enzyme is found in saliva?
a) Pepsin
b) Lipase
c) Salivary amylase
d) Lactase
✅ Answer: c) Salivary amylase -
Pepsin works in the:
a) Mouth
b) Small intestine
c) Stomach
d) Liver
✅ Answer: c) Stomach -
Trypsin works best in:
a) Acidic pH
b) Basic pH
c) Neutral pH
d) Salty solutions
✅ Answer: b) Basic pH -
Lactase is an enzyme that breaks down
a) Sucrose
b) Starch
c) Lactose
d) Fructose
✅ Answer: c) Lactose -
Which enzyme breaks down hydrogen peroxide into water and oxygen?
a) Catalase
b) Oxidase
c) Protease
d) Lipase
✅ Answer: a) Catalase -
Which enzyme breaks down DNA?
a) Nuclease
b) Amylase
c) Protease
d) Lipase
✅ Answer: a) Nuclease -
Which enzyme is used in the dairy industry to make cheese?
a) Pepsin
b) Chymosin
c) Trypsin
d) Amylase
✅ Answer: b) Chymosin -
The enzyme used in detergents to break down stains is
a) Amylase
b) Protease
c) Lipase
d) All of these
✅ Answer: d) All of these -
Enzymes are named by adding which suffix?
a) -ose
b) -ase
c) -ite
d) -zyme
✅ Answer: b) -ase -
Which of the following is not an enzyme?
a) Maltase
b) Glucose
c) Lipase
d) Lactase
✅ Answer: b) Glucose -
Rennin is an enzyme found in:
a) Plants
b) Infants’ stomachs
c) Blood
d) Liver
✅ Answer: b) Infants’ stomachs -
Which of the following breaks down sucrose?
a) Amylase
b) Invertase
c) Lipase
d) Protease
✅ Answer: b) Invertase -
An enzyme that joins molecules together is called:
a) Synthase
b) Ligase
c) Polymerase
d) All of these
✅ Answer: d) All of these -
An enzyme that cuts DNA at specific sites is
a) Restriction enzyme
b) Helicase
c) Polymerase
d) Ligase
✅ Answer: a) Restriction enzyme -
Enzymes responsible for removing phosphate groups are called:
a) Kinases
b) Phosphatases
c) Lipases
d) Amylases
✅ Answer: b) Phosphatases -
DNA polymerase is responsible for:
a) Breaking DNA
b) Synthesizing DNA
c) Destroying DNA
d) Repairing RNA
✅ Answer: b) Synthesizing DNA -
Which of the following enzymes is found in the liver and breaks down toxins?
a) Catalase
b) Pepsin
c) Trypsin
d) Sucrase
✅ Answer: a) Catalase
Section 4: Factors Affecting Enzyme Activity
-
Which of the following can increase enzyme activity up to a limit?
a) Extremely high temperature
b) Moderate increase in temperature
c) Freezing
d) Boiling
✅ Answer: b) Moderate increase in temperature -
Enzymes show maximum activity at:
a) 0°C
b) Room temperature
c) Optimum temperature
d) Any temperature
✅ Answer: c) Optimum temperature -
Extremely high temperature causes enzymes to:
a) Activate
b) Multiply
c) Denature
d) Divide
✅ Answer: c) Denature -
Denaturation of enzymes means:
a) Increasing speed
b) Permanent loss of function
c) Reversible reaction
d) Better efficiency
✅ Answer: b) Permanent loss of function -
The pH value at which an enzyme works best is called:
a) Normal pH
b) Basic pH
c) Optimum pH
d) Extreme pH
✅ Answer: c) Optimum pH -
Pepsin works best in:
a) Neutral pH
b) Alkaline pH
c) Acidic pH
d) Any pH
✅ Answer: c) Acidic pH -
Trypsin works best at:
a) pH 2
b) pH 7
c) pH 8
d) pH 10
✅ Answer: c) pH 8 -
What happens to enzyme activity at very low temperatures?
a) It increases
b) It remains the same
c) It slows down
d) It denatures
✅ Answer: c) It slows down -
The enzyme activity is affected by:
a) pH
b) Temperature
c) Substrate concentration
d) All of these
✅ Answer: d) All of these -
Enzyme activity increases with increasing substrate concentration until:
a) Substrate is used up
b) All enzymes are occupied
c) Reaction ends
d) All of the above
✅ Answer: b) All enzymes are occupied -
Too high or too low pH can:
a) Improve enzyme structure
b) Denature the enzyme
c) Speed up all enzymes
d) Have no effect
✅ Answer: b) Denature the enzyme -
The effect of temperature on enzymes is:
a) Linear
b) Bell-shaped curve
c) No effect
d) Random
✅ Answer: b) Bell-shaped curve -
A graph of enzyme activity vs. temperature shows:
a) Constant rise
b) Constant fall
c) Rise and then sudden drop
d) No change
✅ Answer: c) Rise and then sudden drop -
Low temperature slows enzymes by reducing:
a) Heat
b) Kinetic energy of molecules
c) Enzyme shape
d) Binding
✅ Answer: b) Kinetic energy of molecules -
Substrate concentration affects enzyme activity until:
a) Product forms
b) Enzyme becomes inactive
c) All active sites are full
d) No enzyme remains
✅ Answer: c) All active sites are full -
A higher enzyme concentration usually:
a) Decreases rate
b) Increases rate
c) Has no effect
d) Denatures substrate
✅ Answer: b) Increases rate -
Enzymes are sensitive to:
a) Electric current
b) Environmental conditions
c) Magnetism
d) Color
✅ Answer: b) Environmental conditions -
Which factor is not known to affect enzyme activity?
a) Temperature
b) pH
c) Substrate concentration
d) Light color
✅ Answer: d) Light color -
High substrate concentration results in:
a) Slower reaction
b) No enzyme activity
c) Faster reaction until saturation
d) Instant denaturation
✅ Answer: c) Faster reaction until saturation -
After reaching saturation, adding more substrate:
a) Speeds up the reaction
b) Slows the reaction
c) Has no effect
d) Denatures the enzyme
✅ Answer: c) Has no effect
Section 5: Applications & Biological Importance of Enzymes
-
Enzymes are essential for:
a) Breathing
b) Digestion
c) Circulation
d) Filtration
✅ Answer: b) Digestion -
Without enzymes, metabolic reactions would:
a) Happen faster
b) Not occur at all
c) Occur too slowly to sustain life
d) Produce more energy
✅ Answer: c) Occur too slowly to sustain life -
Enzymes help in:
a) Transporting oxygen
b) Speeding up chemical reactions
c) Carrying nutrients
d) Breaking chromosomes
✅ Answer: b) Speeding up chemical reactions -
In digestion, enzymes break large molecules into:
a) Smaller molecules
b) Ions
c) Atoms
d) Gases
✅ Answer: a) Smaller molecules -
Which of the following industries use enzymes?
a) Food
b) Medicine
c) Textile
d) All of these
✅ Answer: d) All of these -
Enzymes are used in the dairy industry to:
a) Kill bacteria
b) Increase milk production
c) Make cheese and yogurt
d) Cool the milk
✅ Answer: c) Make cheese and yogurt -
Enzymes in washing powders break:
a) Proteins and fats in stains
b) Fibers
c) Threads
d) Buttons
✅ Answer: a) Proteins and fats in stains -
Which enzyme is used in glucose testing strips?
a) Lactase
b) Glucose oxidase
c) Amylase
d) Lipase
✅ Answer: b) Glucose oxidase -
Enzymes in biotechnology are used to:
a) Slow down fermentation
b) Stop DNA replication
c) Cut and paste DNA
d) Color cells
✅ Answer: c) Cut and paste DNA -
Enzymes used in genetic engineering are called:
a) Synthase
b) Ligase and Restriction enzymes
c) Oxidase
d) Protease
✅ Answer: b) Ligase and Restriction enzymes -
Enzymes used to manufacture biofuels are involved in breaking:
a) Metals
b) Carbohydrates
c) Water
d) DNA
✅ Answer: b) Carbohydrates -
Amylase helps convert starch into:
a) Lipids
b) Glucose
c) Fructose
d) Protein
✅ Answer: b) Glucose -
Enzymes used in tenderizing meat are:
a) Proteases
b) Amylases
c) Nucleases
d) Lipases
✅ Answer: a) Proteases -
Which enzyme is used to soften fruits in the food industry?
a) Pectinase
b) Sucrase
c) Lipase
d) Protease
✅ Answer: a) Pectinase -
Enzymes speed up reactions by:
a) Increasing heat
b) Adding pressure
c) Lowering activation energy
d) Removing water
✅ Answer: c) Lowering activation energy -
Which property makes enzymes useful in industries?
a) Flexibility
b) Small size
c) High specificity and efficiency
d) Bright color
✅ Answer: c) High specificity and efficiency -
Enzymes are reused because they are:
a) Very expensive
b) Not changed in the reaction
c) Made of glucose
d) Harmful if left
✅ Answer: b) Not changed in the reaction -
Enzymes used in diagnostic kits help to:
a) Kill viruses
b) Detect chemical changes
c) Generate heat
d) Clean organs
✅ Answer: b) Detect chemical changes -
Biological washing powders contain:
a) Hormones
b) Antibiotics
c) Enzymes
d) Acids
✅ Answer: c) Enzymes -
Enzymes are essential for life because they:
a) Give energy directly
b) Are stored as fat
c) Enable vital reactions to occur fast enough
d) Absorb oxygen
✅ Answer: c) Enable vital reactions to occur fast enough
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